Paper making wire cloth

ABSTRACT

A papermaking wire cloth, especially for the sheet forming zone, includes a paper side ( 12 ) and a backing side ( 14 ). The wire cloth is formed out of at least one type of transverse threads ( 16, 18 ) which are interwoven with at least one type of longitudinal threads ( 20 ). The threads together form repeats (A-H) and at least two different types of crossing ( 22, 24 ). The longitudinal threads ( 20 ) are alternated within the respective repeat (A-H) on the backing side ( 14 ), forming the other type of intersection ( 24 ). The transverse threads ( 18 ) on the backing side ( 14 ) are held on their outer side ( 26 ) which faces the paper side ( 12 ), by at least two longitudinal threads ( 20 ) within the repeat (A-H) on the backing side ( 14 ). Maximum fibre support is achieved on the paper side accompanied by little marking of the upper side as the points of alternation or intersections are evenly distributed.

FIELD OF THE INVENTION

The present invention relates to a papermaking wire cloth, particularlyfor the sheet forming zone, with a paper and a backing side. The wirecloth is made up of at least one type of cross-thread and at least onetype of lengthwise thread interwoven with the former. The threadstogether form at least two different types of crossings. The weavepattern made up of the lengthwise and cross-threads of the paper sidebeing repeated between crossings of the same kind and the lengthwisethreads alternating from the backing side to the paper side andconversely to form the respective other type of crossing.

BACKGROUND OF THE INVENTION

A growing number of high-performance papermaking machines with speeds ofup to 2000 meters per minute and working widths above 10 meters are usedin the paper production industry today. The sheet forming unit is verygenerally designed as a double cloth former, and in many cases as asplit former. Typically, the sheet forming process takes placeimmediately between two papermaking wire cloths in a relatively shortdrainage zone. The time required for sheet formation is reduced tomilliseconds by this short distance and the high production rate. Overthis interval the solid fraction or dry content of the fiber suspensionmust be increased from about 1 percent to about 20 percent. For thepapermaking wire cloth, this requirement means that this machine must becharacterized by very high drainage performance, without leavingmarkings in the paper, and must also provide high fiber support.

Another important point is the transverse stability of wire clothtension. This stability is of decisive importance in determining thethickness and moisture profile of the sheet. Very strict requirementsare set in this connection, particularly for modern machinescharacterized by large operating widths. To improve sheet formation,shaping strips are consequently used with increasing frequency in thesheet forming zone. The shaping strips are mounted alternately on thebacking sides of the wire cloth and are pressed against these sides. Theresult is rapidly alternating load deflection of the cover of the wirecloths in the longitudinal direction.

Today, an effort is customarily made to meet these requirements by useof composite fabrics. A composite fabric used for this purpose isdescribed in DE 42 29 828 C2, for example. The conventional papermakingwire cloth in question has two superposed wire cloth fabrics in the formof single layers interconnected by binding threads extending in thecross and/or lengthwise direction. One of the fabrics is in the form ofdefinition fabric having the mechanical properties of the compositefabric with respect to extension. The other wire cloth fabric in theform of reaction fabric of higher tension and lower rigidity than thedefinition fabric. The wire cloth fabrics include warp threads and woofthreads connected to each other by additional binding threads. As aresult of the design of the cloth fabrics as reaction or definitionfabrics, internal wear, especially wear of the binding threads, isresisted. In this way, the service life of the combination fabric islengthened, and undesirable separation of the wire cloth fabric layer isprevented over a long period. The internal wear of a combination fabricis caused especially by the circumstance that, during redirection of thewire cloth, such as occurs in the area of guiding rollers of the wirecloth batch by way of which the combination fabric is guided, theindividual wire cloth fabric layers are stretched or crushed to varyingdegrees.

Since the binding threads not only belong to the structure of the fabricbut are independent components, they are kept as small as possible indiameter in order to disrupt drainage as little as possible. Withcorrespondingly high stresses, the possibility exists that the thinbinding threads will then break, and the connection between the wirecloth fabrics will be interrupted. In the case of a generic papermakingwire cloth, as disclosed in EP 0 432 413 B1, which also has thestructure of a composite fabric, the proposal has already been made thatbinding threads be used as two fabric-specific threads and interlacedwith the other fabric layer involved to form X-shaped crossings in orderto prevent the disadvantages in the state of the art described. Theaccumulation alone of the known change points in the cross-directionalso results unintentionally in stiffening of the conventional fabric.Considerable differences in length may occur especially over greaterweaving lengths which, in turn, are manifested in difference in tension,with the result that fabric-specific binding threads break and mayresult in failure of the conventional papermaking wire cloth. It is alsoknown in connection with this conventional special type of weave that itis more or less possible to produce only cross-threads of one kind, thatis, cross-threads of more or less the same diameter, for both the upperand the lower fabric, something which reduces the possibility ofefficient support on the backing side. In addition, manufacture of theconventional interlocking fabric is costly.

SUMMARY OF THE INVENTION

Objects of the present invention involve providing papermaking wirecloths having a longer service life available in papermaking and makingthe process more cost-effective.

The alternation of the lengthwise threads is accompanied by formation ofanother type of crossing within each repeat of the backing side. Thecross-threads of the backing side are held by at a minimum of twolengthwise threads within this repeat of the backing side on its outerside facing away from the paper side. Maximum fiber support is achievedon the paper side, along with only slight marking of the upper side,since uniform distribution of the alternating or crossing points isachieved. Since layer binding in the lengthwise direction by all threadsis present, unintentional layer separation is also prevented with highcertainty.

As a result of support on the external side by way of at least twolengthwise threads of a repeat, it is additionally possible to selectcross-threads for the backing side which are thicker than thecross-threads of the paper side and yet to ensure reliable support bythese threads in the papermaking wire cloth. As a result, the supportforces may be usefully increased and the drainage output correspondinglyincreased by relatively “open” backing side formed in this manner.Preferably, a woof ratio of 2:1 is to be chosen. In addition, theoperating time potential for the papermaking wire cloth is maximized bythe long-floating backing side with its wefts widened in cross-section.The high lateral stability is nevertheless achieved on the basis of thetwo separated woof layers.

Other objects, advantages and salient features of the present inventionwill become apparent from the following detailed description, which,taken in conjunction with the annexed drawings, disclose a preferredembodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a partial side view in section of a papermaking wire clothaccording to an embodiment of the present invention;

FIG. 2 is a top plan view in section of the backing side of the wirecloth of FIG. 1, taken along line I—I; and

FIG. 3 is a bottom plan view in section of the backing side of thepapermaking wire cloth of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The drawings illustrate a part of a wire cloth fabric 10 for apapermaking wire cloth (not shown as a whole). It may be used inparticular for the sheet forming zone in conventional papermakingmachines. The wire cloth 10 has a paper side 12 and a backing side 14.The paper side 12 and backing side 14 are formed of two different typesof cross-threads 16 and 18 extending in the cross machine direction, andat least one type of lengthwise thread 20 extending in the machinedirection interwoven with them. The cross-threads 16 and 18 form, withthe lengthwise threads 20 interwoven with them, in both the lengthwiseand the cross directions, as viewed in the line of vision to the wirecloth fabric 10, eight-shank repeats A to H which are repeatedcorrespondingly in the lengthwise and the cross directions. Twodifferent types of X-shaped crossings 22 and 24 are formed within thewire cloth fabric 10 during formation of the repeats A to H (see FIG.1). As is to be seen in FIG. 1, one lengthwise thread 20 of the sametype extends at a crossing 22 of the same type in one direction, forexample, with positive pitch, and with negative pitch at the crossing ofthe other type, 24 in this instance.

As the figures also show, the weave pattern made up of the lengthwisethreads 20 and cross-threads 16 of the paper side 12 is repeated betweencrossings 22 of the same type. The lengthwise threads 20 alternate fromthe backing side 14 to the paper side 12 and vice versa between the twocrossings 22 of the same type, and form the respective other type ofcrossings 24. Consequently, according to the present invention, thatalternation of the lengthwise threads 20, in contrast with the state ofthe art, takes place within the particular repeat A to H of the backingside 14 to form the other type at crossings 24. In addition, asespecially shown in FIG. 3, the cross-threads 18 of the backing side 14are held by at least two lengthwise threads 20 within this repeat A to Hof the backing side on its outer side 26 facing away from the paper side12. The weave of the present invention permits doubling of the number ofwoofs on the paper side 12 relative to the backing side 14 shown. A woofratio of 2:1 is accordingly obtained between paper side 12 and backingside 14. A woof ratio of only 1:1 is generally obtained with theconventional solutions.

The thread diameters which can thus be incorporated on the backing side14 may in this way be doubled in cross-section relative to the paperside 16. This doubling of thread diameters in turn means that the volumeof the material undergoing wear (ground), and accordingly the servicelife of the wire cloth of the present invention, may be increasedconsiderably both by the long-floating weave and the greater diameter onthe backing side 14. In addition, as a result of “open” backing sideachieved, the permeability of the wire cloth fabric 10 is increased todistinctly improve the drainage properties. In the case of thepapermaking wire cloth according to the present invention, allconnecting lengthwise threads 20 are arranged in direct sequence. Incontrast, with the conventional fabric solutions, there is no interposedface weft or face warp. The wire cloth fabric 10 of the presentinvention has a connection pattern largely homogenous in form and areliable connection acting equally in each direction of the fabric. Theweave pattern of the paper side 12 consists of a conventional linenweave which extends between crossings of one kind 22 and the immediatelyfollowing other kind 24, which is of eight-shank configuration.Provision is also made such that the backing side 14 with each repeat Ato H is of eight-shank configuration as viewed in both directions.

The respective lengthwise threads 20, which support the cross-threads 18of the backing side 14 on its outer side 26 facing away from the paperside 12, are mounted so as to be adjacent to each other at least once inpairs (see FIG. 3). It has been found to be especially advantageous fromthe viewpoint of production technology for the cross-threads 16 and 18to be in the form of woof threads and the lengthwise threads 20 in theform of warp threads. As is to be seen in FIG. 1 in particular, thecrossings of one type 22 are supported on the backing side 14 by twocross-threads 18 and the crossing of the other type 24 by fourcross-threads 18 as viewed in the direction of the backing side 14,these supporting cross-threads 18 being positioned more or less in onecommon plane on the outer side 26 of the backing side 14.

In addition, the respective lengthwise threads 20 which adjoin thecross-threads 18 of the backing side 14 on their side facing the paperside 28 (see FIG. 2) are grouped in pairs side by side; up to threegroups may be joined immediately adjacent to each other within a repeatA to H (see cross-thread 18D in FIG. 2). A different, regularlyrepeated, weave pattern is also conceivable in this instance in place ofthe linen weave on the paper side 12. As a result of the equivalentbonding of paper side 12 and backing side 14, a unified texture isprovided rather than, as in the state of the art, a composite fabricmade up of individual fabrics separable from each other. The papermakingwire cloth is nevertheless multilayered in structure and could becorrespondingly augmented to produce a composite fabric.

While various embodiments have been chosen to illustrate the invention,it will be understood by those skilled in the art that various changesand modifications can be made therein without departing from the scopeof the invention as defined in the appended claims.

1. A papermaking wire cloth for a sheet forming zone, comprising: apaper side; a backing side; cross-threads making up said sides; at leastfirst lengthwise threads of at least one type interwoven with saidcross-threads and forming at least first and second crossings whileforming repeats, and first and second crossings being of differenttypes; and a weave pattern formed of said cross-threads and saidlengthwise threads of said paper side being repeated between consecutiveones of said first crossings and consecutive ones of said secondcrossings, said lengthwise threads alternating from said backing side tosaid paper side and vice versa between consecutive ones of said firstcrossings with the second crossing being formed and between consecutiveones of said second crossings with the first crossing being formed, saidlengthwise threads alternating and being formed with a different one ofsaid crossings within one repeat of said backing side, saidcross-threads of said backing side being held within said one repeat ofsaid backing side on an outer side thereof remote from said paper sideby at least two of said lengthwise threads, said weave pattern on saidpaper side being a linen weave.
 2. A papermaking wire cloth according toclaim 1 wherein said linen weave extending between consecutive ones ofsaid first and second crossings is formed of eight shanks.
 3. Apapermaking wire cloth according to claim 1 wherein said backing side isformed with eight shanks within each of said repeats thereof.
 4. Apapermaking wire cloth according to claim 1 wherein said cross-threadsof said backing side are larger in transverse cross section than saidcross-threads of said paper side.
 5. A papermaking wire cloth accordingto claim 1 wherein said cross-threads are woof threads; and saidlengthwise threads are warp threads.
 6. A papermaking wire clothaccording to claim 1 wherein each of said first and second crossing forman X.
 7. A papermaking wire cloth for a sheet forming zone, comprising:a paper side; a backing side; cross-threads making up said sides; atleast five lengthwise threads of at least one type interwoven with saidcross-threads and forming at least first and second crossings whileforming repeats, said first and second crossings being of differenttypes; and a weave pattern formed of said cross-threads and saidlengthwise threads of said paper side being repeated between consecutiveones of said first crossings and consecutive ones of said secondcrossings, said lengthwise threads alternating from said backing side tosaid paper side and vice versa between consecutive ones of said firstcrossings with the second crossing being formed and between consecutiveones of said second crossings with the first crossing being formed, saidlengthwise threads alternating and being formed with a different one ofsaid crossings within one repeat of said backing side, saidcross-threads of said backing side being held within said one repeat ofsaid backing side on an outer side thereof remote from said paper sideby at least two of said lengthwise threads, side lengthwise threadssupporting said cross-threads of said backing side on said outer sidethereof being positioned at least once in pairs adjacent one another. 8.A papermaking wire cloth according to claim 7 wherein said lengthwisethreads delimiting said cross-threads of said backing side on a sidethereof facing away from said paper side are present in up to threegroups, said cross-threads of said backing side being grouped in pairswith one thread of each pair being next to the other thread of eachpair.
 9. A papermaking wire cloth for a sheet forming zone, comprising:a paper side; a backing side; cross-threads making up said sides; atleast first lengthwise threads of at least one type interwoven with saidcross-threads and forming at least first and second crossings whileforming repeats, said first and second crossings being of differenttypes; and a weave pattern formed of said cross-threads and saidlengthwise threads of said paper side being repeated between consecutiveones of said first crossings and consecutive ones of said secondcrossings, said lengthwise threads alternating from said backing side tosaid paper side and vice versa between consecutive ones of said firstcrossings with the second crossing being formed and between consecutiveones of said second crossings with the first crossing being formed, saidlengthwise threads alternating and being formed with a different one ofsaid crossings within one repeat of said backing side, saidcross-threads of said backing side being held within said one repeat ofsaid backing side on an outer side thereof remote from said paper sideby at least two of said lengthwise threads, each of said first crossingsbeing supported on said backing side by two of said cross-threads, eachof said second crossings being supported on said backing side by four ofsaid cross-threads, said cross-threads supporting said crossings beingpositioned in a common plane on said outer side.
 10. A papermaking wirecloth for a sheet forming zone, comprising: a paper side; a backingside; first and second cross-threads making up said paper and backingsides, respectively; lengthwise threads of at least one type interwovenwith said first and second cross-threads and forming at least first andsecond crossings while forming repeats, said first and second crossingsbeing of different types; and a weave pattern formed of said firstcross-threads and said lengthwise threads on said paper side beingrepeated between consecutive ones of said first crossings andconsecutive ones of said second crossings, said lengthwise threadsalternating from said backing side to said paper side and vice versabetween consecutive ones of said first crossings with the secondcrossing being formed therebetween and between consecutive ones of saidsecond crossins with the first crossing being formed therebetween, saidlengthwise threads alternating and being formed with each different oneof said crossings within one repeat of said backing side, said secondcross-threads being held within said one repeat on an outer side of saidbacking side remote from said paper side by at least two of saidlengthwise threads, said weave pattern on said paper side being a linenweave.
 11. A papermaking wire cloth according to claim 10 wherein saidlinen weave extending between consecutive ones of said first and secondcrossings is formed of eight shanks.
 12. A papermaking wire clothaccording to claim 10 wherein said backing side is formed with eightshanks within each of said repeats thereof.
 13. A papermaking wire clothfor a sheet forming zone, comprising: a paper side; a backing side;first and second cross-threads making up said paper and backing sides,respectively; lengthwise threads of at least one type interwoven withsaid first and second cross-threads and forming at least first andsecond crossings while forming repeats, said first and second crossingsbeing of different types; and a weave pattern formed of said firstcross-threads and said lengthwise threads of said paper side beingrepeated between consecutive ones of said first crossings andconsecutive ones of said second crossings, said lengthwise threadsalternating from said backing side to said paper side and vice versabetween consecutive ones of said first crossings with the secondcrossing being formed therebetween and between consecutive ones of saidsecond crossings with the first crossing being formed therebetween, saidlengthwise threads alternating and being formed with each different oneof said crossings within one repeat of said backing side, said secondcross-threads being held with said one repeat on an outer side of saidbacking side remote from said paper side by at least two of saidlengthwise threads, said lengthwise threads supporting said secondcross-threads being positioned at least once in pair adjacent oneanother.
 14. A papermaking wire cloth according to claim 10 wherein saidsecond cross-threads are larger in transverse cross section than saidfirst cross-threads.
 15. A papermaking wire cloth according to claim 10wherein said cross-threads are woof threads; and said lengthwise threadsare warp threads.
 16. A papermaking wire cloth according to claim 10wherein each of said first and second crossings form an X.
 17. Apapermaking wire cloth according to claim 13 wherein said lengthwisethreads delimiting said second cross-threads are present in up to threegroups, said second cross-threads being grouped in pairs with one threadof each pair being next to the other thread of each pair.
 18. Apapermaking wire cloth for a sheet forming zone, comprising: a paperside; a backing side; first and second cross-threads making up saidpaper and backing sides, respectively; lengthwise threads of at leastone type interwoven with said first and second cross-threads and formingat least first and second crossings while forming repeats, said firstand second crossings being of different types; and a weave patternformed of said first cross-threads and said lenghtwise threads on saidpaper side being repeated between consecutive ones of said firstcrossings and consecutive ones of said second crossings, said lengthwisethreads alternating from said backing side to said paper side and viceversa between consecutive ones of said first crossings with the secondcrossing being formed therebetween and between consecutive ones of saidsecond crossings with the first crossing being formed therebetween, saidlengthwise threads alternating and being formed with each different oneof said crossings within one repeat of said backing side, said secondcross-threads being held within said one repeat on an outer side of saidbacking side remote from said paper side by at least two of saidlengthwise threads, each of said first crossings being supported on saidbacking side by two of said second cross-threads each of said secondcrossings being supported on said backing side by four of said secondcross-threads, said second cross-threads supporting said first andsecond crossings positioned in a common plane on said outer side.